Device and method for wavefront measurement of an optical imaging system, and a microlithography projection exposure machine

Abstract

A device and a method for wavefront measurement of an optical imaging system, and a microlithography projection exposure machine that is equipped with such a device. The device has a wavefront generating unit that includes an optical element ( 1 ) with an object-side periodic structure ( 2 ), and a light source unit ( 20,21 ) for illuminating the object-side periodic structure with the aid of a measuring radiation. The device also has a detector unit that is arranged on the image side of the imaging system to be measured and that includes an optical element ( 3 ) with an image-side periodic structure, and a detector element ( 52, 52 a , 52 b ) for detecting an overlay pattern of the imaged object-side periodic structure and image-side periodic structure. The wavefront generating unit is designed to restrict the angular spectrum ( 6 ) of the measuring radiation emanating from a respective field point ( 7 ), the design being such that the measuring radiation emanating from the respective field point illuminates only in each case a specific subregion of a pupil plane of the optical imaging system.

1. A device for wavefront measurement of an optical imaging system, comprising:
 a wavefront generating unit arranged on the object side of the imaging system to be measured and comprises an optical element with an object-side periodic structure and a light source unit for illuminating the object-side periodic structure with the aid of a measuring radiation, and 
 a detector unit arranged on the image side of the imaging system to be measured and comprises an optical element with an image-side periodic structure and a detector element for detecting an overlay pattern of the imaged object-side periodic structure and image-side periodic structure, 
 wherein the wavefront generating unit is designed to restrict the angular spectrum of the measuring radiation emanating from a field point, the design being such that at least the measuring radiation emanating from a first and a second field point respectively illuminates only a subregion of a pupil plane of the optical imaging system, and wherein the pupil subregion belonging to the first field point at most partially overlaps the pupil subregion belonging to the second field point. 
 
     
     
       2. The device as claimed in  claim 1 , wherein at least one of the optical element with the object-side structure and the optical element with the image-side periodic structure is assigned a displacing unit for lateral displacement along at least one periodicity direction. 
     
     
       3. The device as claimed in  claim 1 , wherein the light source unit comprises at least one point light source that is positioned at a spacing in front of the optical element with the object-side periodic structure such that the at least one point-light source illuminates assigned field points with an appropriately restricted angular spectrum. 
     
     
       4. The device as claimed in  claim 3 , wherein the light source unit comprises a single point light source that is positioned at a spacing in front of the optical element with the object-side periodic structure such that the associated illuminating angle thereof is at least substantially equal to the input-side numerical aperture of the optical imaging system. 
     
     
       5. The device as claimed in  claim 1 , wherein the light source unit comprises at least one extended light source, positioned in front of the optical element with the object-side periodic structure, as well as a pinhole diaphragm unit with at least one pinhole that is positioned behind the optical element with the object-side periodic structure. 
     
     
       6. The device as claimed in  claim 1 , wherein the image-side periodic structure is located on a detector surface of the detector element. 
     
     
       7. The device as claimed in  claim 1 , wherein the image-side periodic structure is located on a substrate configured to be moved laterally relative to a detector surface of the detector element. 
     
     
       8. The device as claimed in  claim 1 , further comprising a substrate and a detector optical unit, located downstream of the substrate, for imaging the overlay pattern onto a detector surface of the detector element. 
     
     
       9. The device as claimed in  claim 1 , wherein the first and the second periodic structure each include a moiré structure with one or two periodicity directions. 
     
     
       10. A method for wavefront measurement of an optical imaging system having a device as claimed in  claim 1 , comprising:
 positioning the optical element with the object-side structure in an object plane, and positioning the optical element with the image-side structure in an image plane of the optical imaging system, 
 producing overlay patterns of imaged object-side periodic structure and image-side periodic structure, and detecting these patterns by means of the detector element, 
 calculating the spatial derivatives of the wavefront from one or more overlay patterns at different interpolation points that correspond to the pupil subregions illuminated from the respective field point, and 
 reconstructing the course of the wavefront from the wavefront derivatives at the interpolation points. 
 
     
     
       11. The method as claimed in  claim 10 , wherein at least one of the optical element with the object-side structure and the optical element with the image-side structure is displaced laterally along a periodicity direction in order to produce overlay patterns with a different phase offset. 
     
     
       12. The method as claimed in  claim 10 , wherein the device for wavefront detection is calibrated before carrying out the wavefront measurement. 
     
     
       13. The method as claimed in  claim 10 , wherein, in order to determine phase information from the respective overlay pattern at an interpolation point, the intensity of the incident measuring radiation is averaged over an area of the detector surface that is assigned to the interpolation point and is greater than a period length of the periodic structures. 
     
     
       14. A microlithography projection exposure machine comprising:
 a projection lens, and 
 a device for wavefront measurement at the projection lens as claimed in  claim 1 .